1. Field of the Invention
The present invention relates to gas fluidized bed processes for producing ethylene propylene diene monomer resins which contain ethylidene norbornene therein and more particularly to a process for reducing the odor of ethylidene norbornene present in such resins.
2. Description of the Prior Art
The introduction of high activity Ziegler-Natta catalyst systems has lead to the development of new polymerization processes based on gas phase reactors such as disclosed in U.S. Pat. No. 4,482,687 issued Nov. 13, 1984. These processes offer many advantages over bulk monomer slurry processes or solvent processes. They are more economical and inherently safer in that they eliminate the need to handle and recover large quantities of solvent while advantageously providing low pressure process operation.
The versatility of the gas phase fluid bed reactor has contributed to its rapid acceptance. Alpha-olefin polymers produced in this type of reactor cover a wide range of density, molecular weight distribution and melt indexes. In fact new and better products have been synthesized in gas phase reactors because of the flexibility and adaptability of the gas phase reactor to a large spectrum of operating conditions. More recently, the gas phase fluid bed reactor has been extended to the production of rubbery resins such as ethylene propylene diene monomer such as disclosed in U.S. Pat. No. 4,710,538 issued Dec. 1, 1987.
Ethylene propylene diene monomer (EPDM) resins are presently produce by a variety of techniques. In certain processes for producing EPDM resins, the amount of ethylidene norbornene monomer remaining in the finished polymer, (i.e, after completion of the devolatilization process to remove the monomer from the polymer,) in a free form is such as to cause objectionable odors.
Thus when producing and recovering EPDM resin according to certain of the above processes, there still exists a somewhat objectionable odor in the resins product. This is primarily due to the fact that ethylidene norbornene (ENB), a monomer used for sulfur curable ethylene propylene rubbers, has a very distinctive an objectionable odor and is present in minute quantities in the finished product. Ethylidene norbornene can be detected by humans at concentrations as low as 14 ppbv. For example, in a typical fluidized bed process EPDM resins contain as much as 5% by weight of dissolved ENB. Conventional procedures for removing ENB are still not satisfactory for reducing the ENB content to acceptable levels.
Zeolites in general have been employed in the past for removal of residual isocynate from urethane polymers (See Japanese Kokai JP 52/53999 [77/53999], 30 Apr. 1977.
Hungarian Patent HU 41425A2, issued Apr. 28, 1987 discloses the use of zeolites as dielectricheating promoters, for cross-linking of rubber and polyolefin compounds by microwave irradiation.
Zeolites have also been disclosed as fillers for synthetic rubbers in tire manufacturing and zeolite amine adducts have been employed to improve the properties resulting from the curing process of sulfur based rubber compounds as well as the vulcanization rates of such products (see for example East German patent DD 242047 and DD 224322 issued 14 Jan. 1987 and 3 July 1985 respectively).
U.S. Pat. No. 4,795,482 issued to Gioffre et. al. on Jan. 3, 1989 and assigned to Union Carbide Corporation discloses a process for eliminating organic odors. Removal of ENB odors resulting from a gas fluidized bed process for producing EPDM resins nor the specific manner of introducing said materials is not disclosed or suggested.
It has been discovered that a specific type of zeolite when utilized in a particular manner is extremely effective in reducing the amount of ethylidene norbornene present in EPDM resins.